Dybbuk

From Mordenkainen's Tome of Foes (2016):

Dybbuks terrorize mortals on the Material Plane by possessing corpses and giving them a semblance of life, after which the demons use them to engage in a range of sordid activities.

Puppet Masters. In their natural form, dybbuks appear as translucent flying jellyfish, trailing long tendrils as they move through the air. They rarely travel in this fashion, however. Instead, a dybbuk possesses the first suitable corpse it finds, rousing the body from death so it can then indulge its hideous vices.

Dark Masquerade. By plundering a corpse’s memories and accessing its capabilities, a dybbuk can impersonate the creature as it was in life. But the truth of the matter quickly becomes apparent to those around it, because a dybbuk can’t resist pursuing its vices with a maniacal single-mindedness that betrays its true nature. Dybbuks delight in terrorizing other creatures by making their host bodies behave in horrifying ways — throwing up gouts of blood, excreting piles of squirming maggots, and contorting their limbs in impossible ways as they scuttle across the ground.

From D&D 3.5e Fiendish Codex I: Hordes of the Abyss (2006):

Loumara Subtype: The loumaras represent an emergent demonic subtype and are fairly recent additions to the Abyss. Even so, they have plagued the Material Plane for ages. These demons rise from the fragmenting dreams of dead gods found in the Dreaming Gulf (layer 230), spreading out into the surrounding Abyss like a stain or slipping into the Material Plane through tiny tears in reality. Their indistinct nature and lack of physical forms has resulted in obscurity on the Material Plane, yet their taint in the mortal realm is far greater than most would imagine. Only two kinds of loumaras have thus far manifested with any regularity: the corpse-haunting dybbuks and the murderous guecubus. 

Loumara Traits: A loumara has the following traits (unless otherwise noted in a creature’s entry). 

 —Immunity to acid, electricity, and fire.  

—Resistance to cold 10.  

—Incorporeal: All loumaras have the incorporeal subtype when not possessing a physical body.  

—Possession (Su): All loumaras can possess physical objects or creatures. The exact kind of object or creature a specifi c loumara can possess is noted in the creature’s description.

Dybbuk Intro: A faint brush of cold, the fl eeting scent of moldering lilies, and a sudden conviction of loss mark the passage of this indistinct shape. Its form is visible only as a flickering shimmer in the air accompanied by faint tendrils of pale smoke.

Disembodied intelligences spawned by the Abyss, dybbuks must possess the dead to work their evil.

A dybbuk in its natural form constantly scours its environment for a suitable host body. It knows that it can be killed when it is without a host and avoids combat as a result. Once it inhabits a body, it apes that body’s normal activities, although this is more of a means to an end (finding a better body) rather than being indicative of any real need to eat, sleep, or otherwise behave as a living creature should. 

Dybbuks are found in the Abyss at sites of great battles or near large graveyards. They are not fond of regions heavily populated with undead, since they have no use for bodies that are already animated. 

A dybbuk’s driving need is its eternal search for a perfect body. To a dybbuk, a perfect body is one that is undamaged from violence, quite handsome or beautiful for its race, and has many links to its society’s leadership. A dybbuk hopes to possess such a perfect body before anyone discovers the victim has died, so that it can go on living the victim’s life without arousing suspicion. Once a dybbuk has found a perfect body, it allows itself to be overtaken by that society’s sins and vices, plunging hedonistically into depravity until its body is ruined or it is otherwise forced to abandon its plaything.

Much of a dybbuk’s existence actually consists of leapfrogging from lesser body to lesser body. It sees these bodies as stepping stones, with each transfer to a new body putting it closer to its intended target. A dybbuk typically has a specifi c person targeted as a perfect body and does what it can to get closer to this targeted victim, with the goal of either engineering the person’s accidental death or catching the victim alone (in which case it uses its death touch to kill its target).